The present invention relates to an illuminating light supply system in an electronic endoscope apparatus in which an endoscope is connected to a monitor television.
A known electronic endoscope apparatus will be briefly described. An inserting portion of an endoscope is inserted into a subject to be inspected such as a body cavity of a patient, interior of machines, interior of piping or the like, for example. Illuminate-light is irradiated through an illuminating window provided at a distal end of the inserting portion. The light reflected from a wall surface of the body cavity enters through a viewing window provided at the distal end of the inserting portion, and is received by a light receiving portion of a solid state image pickup element such as CCD (charge coupled device) arranged within the distal end of the inserting portion and adjacent the viewing window. The light received by the image pickup element is photoelectrically converted into image signals. The image signals are converted into television picture signals by a picture circuit connected to the image pickup element, and the picture signals are supplied to a monitor television on which images of the interior of the body cavity are displayed.
More specifically, in the aforesaid monitor television, an interlaced scanning is performed similarly to general television machines, i.e., one frame scanning is performed by an odd field scanning and an even field scanning. Firstly, the horizontal scannings are coarsely performed by the odd field scanning, and then areas between pairs of adjacent horizontal scanning lines are horizontally scanned by the even field scanning.
A vertical synchronizing signal is generated by the picture circuit during a short blanking period between each pair of adjacent field scanning durations and, immediately thereafter, a transfer command signal is sent from the picture circuit to the image pickup element. In the image pickup element, in response to the transfer command signal, electric charge representative of the image signal of each of the picture elements obtained by the light receiving portion is transferred at a time to a memory portion of the image pickup element. The transfer time is very short and is on the order of 0.1 msec. The image signals to be offered to each field scanning are sent from the memory portion of the image pickup element to the picture circuit where the television picture signals for the odd and even field scannings are alternately outputted on the basis of the image signals.
When a precise diagnosis is required, a frame memory is utilized to store television picture signals corresponding to one frame scanning, and stationary pictures are projected on the monitor television on the basis of the stored television picture signals. This permits the stationary pictures to be viewed, recorded on an optical disc, or photographed by a camera.
However, the stationary pictures are not so much clear, and it is difficult to precisely conduct the diagnosis. The reasons for this will be discussed below.
The illuminating light is continuously irradiated into the body cavity through the illuminating window. Each picture element in the light receiving portion of the image pickup element continuously receives the reflected light for one field scanning duration (1/60 second), and the electirc charge corresponding to an integrated value of the amount of light received is stored in the memory portion of the image pickup element. Consequently, an amount of movement of the subject to be viewed during one field scanning time is stored as blur of the image, and the picture per se corresponding to one field scanning cannot have sufficient sharpness. This resembles, in principle, the relationship between opening time of a shutter and shapness of a photographed image of a camera. That is, in the camera, since the image information is continuously stored on a film for a time period during which the shutter is opened, should the opening time be long, the image of a subject to be photographed which is fast in movement would be blurred.
Furthermore, since the stationary picture projected on the monitor television is constituted by the overlap of the respective pictures due to two, i.e., odd and even field scannings, the amount of movement of the subject to be viewed corresponding to one frame scanning time (1/30 second) inevitably appears as blur.